Chevrolet 70 Series 1970, Service Manual

Page: 405 / 841

53 AND 71 SERIES DIESEL ENGINES 6C-8
Figure 10—Adjusting Engine Idle
IMPORTANT: It may be n e c e ssa r y to turn
buffer sc r e w in sligh tly to reduce su rge or r o ll in
engine. Do not in c r e a se engine rpm with buffer
scr ew .
2. If n e c e ssa r y to adjust idle speed, loosen
lo ck nut and turn idle adjusting sc rew IN to in ­
c r e a s e or OUT to d ec rea se (fig. 10). Lock adjust­
ing sc r e w with lock nut when idle sp eed is approx­
im ately 15 rpm below d esired settin g. The reco m ­
mended id le sp eed is 500 rpm.
ADJUST BUFFER SCREW
IMPORTANT: Turning buffer sc r e w in too far
w ill cau se the engine to run at e x c e s s iv e speed
making it difficult to sh ift axle and or tra n sm issio n .
With the id le speed adjusted, and engine at
operating tem perature adjust buffer spring screw
a s follow s:
1. Turn the buffer sc r e w in (fig. 11) so it
contacts the d ifferen tial le v e r a s lightly as p o s­
s ib le and s t ill elim in a tes the engine r o ll or su rg e.
Figure 11 —Adjusting Buffer Screw
NOTE: Do not in c r e a se engine idle sp eed m ore
than 15 rpm with the buffer screw .
2. Hold buffer sc r e w and tighten the lock nut.
3. Buffer sc r e w can be checked fo r proper
adjustment by acceleratin g engine and d e -a c c e le r -
ating. When engine com es back to id le on d e -a c c e l­
eration it should r o ll one to two tim es and then
le v e l off to steady id le speed. If engine r o lls or
su rg es m ore than two tim e s the buffer scr ew needs
to be adjusted sligh tly in. If the engine does not
ro ll or su rge one to two tim es the sc r e w is in too
fa r. Adjust if n e c e ssa r y .
4. R echeck the m aximum no-load sp eed . If it
has in crea sed m ore than 25 rpm , back off the
buffer sc r e w until the in c r e a se is l e s s than 25 rpm.
5. in sta ll governor spring housing co v er (fig.
4) with two attaching sc r e w s .
6. Install throttle and stop linkage to governor
cover le v e r s .
7. Check throttle and stop linkage fo r proper
adjustm ent a s shown in ENGINE FUEL SYSTEM
(SEC. 6M) of this manual.
6V-53 DIESEL ENGINE TUNE-UP CHART
Engine T y p e ........................... 6V-53 (2 Stroke Cycle)
Number of C y l i n d e r s ...................................................
6
C ylinder Numbering ........................... (See Figure 2)
F irin g Order ........................... 1 L -3R -3L -2R -2L -1R
V alve L ash ............... 0.024" (Hot) or 0.026" (Cold)
C ylinder Head B olt Torque . . . 190-200 F t.-L b s.*
Engine Idle Speed .......................................... 500 Rpm
Engine Governed Speed
Full L o a d ............ ...................................... 2600 Rpm
No L o a d ...................................................... 2750 Rpm
Fuel Injector Type ................................................... N45
Injector Valve Opening P r e ssu r e . 2000-3200 P s i.
C om pression Ratio ................................................ 21:1
Cylinder C o m p r e s s io n ................................. 540 Psi**
Injector Tim ing D im e n s io n ........................ 1.460"***
Fuel Supply Pump
Capacity
(At 1500 Engine Rpm) . . . . 90 Gal. P e r Hr.
R e lie f Valve Opens
(Max. L bs. P r e ssu r e ) ....................................75
* Threads and bolt heads coated with International Compound #2 (P art No. 5198563).
** With engine running at 600 rpm. V ariation between cylin d ers not to exceed 25 p si.
*** U se in jector tim ing gauge No. J-1853.
CHEVROLET SERIES 70-90 HEAVY DUTY TRUCK SHOP MANUAL